This invention relates to a pump shaft sealing system and to a pump having such a shaft sealing system.
There are a large number of different shaft sealing systems used with fluid handling pumps that are very satisfactory for normal operating conditions and for conventional centrifugal pumps. In some situations such on ships, centrifugal pumps are used to pump wastes from toilets, kitchens and various and sundry liquids having caustic or toxic chemicals. Leakage from such pumps presents an especially hazardous situation if the leakage is contained in the pumping compartment in the proximity of the ship's crew by exposing them to infectious and/or contagious diseases, such as hepatitis. Conventional centrifugal pumps on ships may have shaft seal systems that initially leak only a few drops per day. With time, the leakage becomes so pronounced that the constant clean-up of the leaked material and the sterilization of the contaminated area becomes so burdensome, that the leaking system has to be replaced. On most vessels, this replacement process interferes with the normal operation of the ship, since toilets, kitchen sinks and other liquid discharge systems must be shut down during the process. The entire replacement process may take several hours or days. The pump and shaft seal parts are contaminated and must therefore be handled with care so that the ship's crew is not infected during the seal replacement process. Thus, there is a need for a new and improved shaft seal system for pumps used in such or similar environments.
Another difficult environment for pump shaft sealing systems is that of pumping slurries, such as high solid content slurries in mining, dredging or sludge removal. In mining and dredging operations, there are often high concentrations of very fine, sharp and/or hard particles that slide between the rotating shaft and the stationary seal surfaces. To prevent premature wear due to excessive friction, these sealing surfaces must be lubricated. In conventional stuffing boxes, water is often used as a lubricant between a thin copper seal element and the rotating shaft surface. In other systems, grease or some other lubricant is injected into the shaft seal system continuously or at periodic intervals to lubricate the seal surfaces. A common shaft seal ring is made from a VITON.TM. material, which is a registered trademark of DuPont Industries. The lip of the VITON.TM. seal ring is urged by springs against the shaft with a predetermined force. Even with lubricant between the VITON.TM. seal element and the rotating shaft, the friction may cause the seal temperature to rise, and the seal would degrade and fail if it were not of a material capable of operating at high temperatures for long periods of time. Chemicals in the liquid being pumped also can cause material degradation particularly when the seal material is raised to a high elevated temperature. The failure of shaft seal systems can lead to considerable maintenance costs and loss of valuable production time in dredging, mining and other pumping operations. Thus, there is a need for an improved shaft sealing for these kind of pumping operations.
Conventional centrifugal liquid pumps use a net positive suction head in the pump housing to force the liquid to flow through the pump housing outlet. If air is introduced into the pump casing in sufficient quantities, the pressure differential is lost and the pump is said to cavitate in that it no longer is pumping liquid. In centrifugal liquid pumps, the positive pressure in the seal area tends to push liquids and foreign materials, such as particles of dirt or sand along the pump shaft and with possibility into the shaft bearings, thereby damaging the bearings. Another type of pump is called the Eddy Pump and disclosed in U.S. Pat. Nos. 4,596,511 and 4,792,275 (which is a registered trademark of Eddy Pump Corporation of Santee, Calif. The Eddy Pump produces a negative pressure within the pump seal area. This negative pressure is the result of a rotating rotor that forms a rotating liquid nucleus within the housing. The Eddy Pump does not have a closely related rotor and casing, as do centrifugal pumps. The negative pressure in the Eddy Pump will be communicated into and through the shaft seal. There is a need for a new and improved shaft seal system for use with such Eddy Pumps particularly in demanding environmental applications, as discussed herein.